It is occasionally desirable to remove air from the interior of a fluid system to the exterior of the fluid system through an air valve. In many cases, it is also desirable that air from the exterior of the fluid system be prevented from entering the fluid system through the same air valve when air is not being removed from the interior of the fluid system through the air valve. When air is being removed from the fluid system, the air valve is open, and when air is not being removed from the fluid system, the air valve is closed. Over time, seals in the air valve may deteriorate in quality and effectiveness after repetitive operation of the air valve or under a wide range of fluid and fluid system conditions. Violent closure of the air valve is also possible under certain conditions, which can also cause damage to an air valve seal. In addition, a seal that is suitable for only one small range of pressures or one type of fluid system has limited use. Even though the fluid type and certain factors may be known, the fluid pressure, the frequency of air valve operation, and other variables may vary or may be unknown for a particular fluid system.